linux-kernel - Re: [tip:x86/mm] x86/fault: Decode and print #PF oops in human readable form

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Date:   Sun, 21 Apr 2019 20:35:24 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     hpa@...or.com, torvalds@...ux-foundation.org, luto@...nel.org,
        sean.j.christopherson@...el.com, peterz@...radead.org,
        tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        riel@...riel.com, dave.hansen@...ux.intel.com,
        yu-cheng.yu@...el.com
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/fault: Decode and print #PF oops in human
 readable form

On Fri, Apr 19, 2019 at 11:35:51AM -0700, tip-bot for Sean Christopherson wrote:
>     BUG: kernel NULL pointer dereference, address = 0000000000000008
>     #PF: supervisor-privileged instruction fetch from kernel code
>     #PF: error_code(0x0010) - not-present page
> 
>     BUG: unable to handle page fault for address = ffffbeef00000000
>     #PF: supervisor-privileged instruction fetch from kernel code
>     #PF: error_code(0x0010) - not-present page
> 
>     BUG: unable to handle page fault for address = ffffc90000230000
>     #PF: supervisor-privileged write access from kernel code
>     #PF: error_code(0x000b) - reserved bit violation

Writing those in human-readable form is nice. May I suggest making those
messages more succinct, though - we'll be staring at them for years,
after all.

---
From: Borislav Petkov <bp@...e.de>
Date: Sun, 21 Apr 2019 20:24:08 +0200
Subject: [PATCH] x86/fault: Make fault messages more succinct

So we are going to be staring at those in the next years, let's make
them more succinct. In particular:

 - change "address = " to "address: "
 - "-privileged" reads funny. It should be simply "kernel" or "user"
 - "from kernel code" reads funny too. "kernel mode" or "user mode" is
   more natural.

An actual example says more than 1000 words, of course:

  [    0.248370] BUG: kernel NULL pointer dereference, address: 00000000000005b8
  [    0.249120] #PF: supervisor write access in kernel mode
  [    0.249717] #PF: error_code(0x0002) - not-present page

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/mm/fault.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 74c9204c5751..a0df19b0897d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -630,13 +630,13 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long ad
 	}
 
 	if (address < PAGE_SIZE && !user_mode(regs))
-		pr_alert("BUG: kernel NULL pointer dereference, address = %px\n",
+		pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
 			(void *)address);
 	else
-		pr_alert("BUG: unable to handle page fault for address = %px\n",
+		pr_alert("BUG: unable to handle page fault for address: %px\n",
 			(void *)address);
 
-	pr_alert("#PF: %s-privileged %s from %s code\n",
+	pr_alert("#PF: %s %s in %s mode\n",
 		 (error_code & X86_PF_USER)  ? "user" : "supervisor",
 		 (error_code & X86_PF_INSTR) ? "instruction fetch" :
 		 (error_code & X86_PF_WRITE) ? "write access" :
-- 
2.21.0

-- 
Regards/Gruss,
    Boris.

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